Its purpose is in particular to propose a particular embodiment of lights which, whilst comprising a shield intended to prevent diffusion of light upwards, obtains a sufficient light intensity for satisfactory viewing of certain elements placed in various areas situated above a central axis of the beam emitted by the light.
The field of the invention is, in general terms, that of automobile lights. In this field, various types of light are known, amongst which there are essentially:                side lights, of low intensity and range;        dipped lights, of higher intensity and with a range on the road of approximately 70 meters, which are used essentially at night and where the distribution of the light beam is such that it does not dazzle the driver of a vehicle being passed;        long-range driving lights, and additional lights of the long-range type, where the area of vision of the road is around 200 meters, and which must be switched off when passing another vehicle in order not to dazzle its driver;Overhead light corresponds to the French term; “Point de Portique”vehicle in order not to dazzle its driver;        fog lights.        
The light device according to the invention is more particularly intended to be used as a dipped light, but the particularity of its structure, and in particular its projection lens, could be reproduced on other types of light in order to meet various requirements.
In the state of the art, essentially two types of light each having a distinct structure are known for dipped lights.
The first type of light is composed essentially of a reflector associated with a light source. The reflector consists of a mirror comprising a set of serrations, or areas of various shapes, thus producing a complex surface whose form, which was previously the subject of precise calculations, reflects the light signals emitted by the light source in order to produce a light beam essentially oriented horizontally and downwards.
The second type of light is illustrated in FIG. 1. This figure depicts a side view in section of a dipped light 100 known from the state of the art. A dipped light of this type comprises essentially a reflector 101, a light source 102, radiating a power in the form of emitted light signals 103, disposed close to the top of the reflector 101, and an exit surface 104 for a light beam 106. The exit surface 104 can for example be a glass of the plastic type; it preferably does not have any optical properties, that is to say it does not divert the light rays passing through it, or only a little.
Before reaching the exit surface 104, the light signals 103 are caused to pass through a lens 105 either directly or after reflection on the reflector 101. This lens is usually of the convex circular type. It is called a projection lens. It has an entry face 110 and an exit face 111. It diffuses the light beam 106, whose orientation and range depend in particular on the arrangement of the lens 105 within the projection device 100 and the optical characteristics of the lens 105. A central part of the light source 102 is preferably disposed in the focal area of a first focus F1 of the reflector 101, and the focus of the projection lens 105 is situated in the focal area of a second focus F2 of the reflector 101. Thus a light signal 103 emitted by the central part of the light source 102 will pass through the second focus F2 of the reflector 101 and will leave the projection lens 105 horizontally or approximately horizontally. With the exception of the light signals which are reflected on ends 107 of the reflector 101, all the light signals 103 emitted by the central part of the light source 102 converge towards the second focus F2.
In general terms, the expression light signals is used for all the light signals emitted by the light source 102, and light beams for all the light beams which are actually emitted by a light at the exit surface 104, or at the projection lens 105.
In this second type of light, a shield 108 is interposed between the reflector 101 and the projection lens 105. The shield 108 is disposed in a plane parallel to the projection lens 105, approximately level with the object focal plane of the lens, so that the image of the shield is emitted to infinity. By virtue of the presence of such a shield 108, the light beam 106 which is actually emitted by the light device 100 is not emitted above a cutoff line determined by the shape of an upper part 109 of the shield 108.
FIG. 2 gives an example of the form 200 of the light beam 106 projected on a screen. A cutoff line 201 marks the boundary between a bottom area where the light intensity is sufficient to illuminate the road and satisfy the various regulations laid down and an upper area where the light intensity is almost zero. The cutoff line 201 has a change in height at a central axis 203 of the beam. The form 201 depicted, with a light beam higher on the right-hand part of the projection, corresponds to that of a vehicle light traveling in a country where travel is required on the right. In a country where travel is required on the left, a form would be obtained which, with respect to a vertical axis 202, would be symmetrical with that shown.
The two types of light described are available today on the market. Vehicle manufacturers choose one or other of these types of light essentially according to aesthetic criteria, the two types of light not having the same appearance.
However, a problem is posed with the second type of light described. This is because, though it is true that the light intensity must be low above the cutoff line 201, the various regulations nevertheless require that a minimum light intensity be emitted in certain directions situated above the cutoff 201. In particular, various regulations require a minimum light intensity at certain points situated above the cutoff line, these points being called overhead lights, since they correspond approximately to points in the vicinity of which there are situated panels of the motorway panel type when these panels are at a given visibility distance from the vehicle. For example, in American regulations, four overhead lights are found which are respectively situated at 2u4l, 4u8l, 2u4r and 4u8r with respect to the optical axis of the lens, the figures corresponding to degrees, “u” corresponding to “up”, “l” corresponding to left and “r” corresponding to right.
Various solutions have been proposed in the state of the art for illuminating these overhead lights whilst keeping the shield 108 in the projector device.
A first solution consists of providing a hole in the shield 108. If this hole is disposed at the correct point, an approximately rectangular illuminated area above the cutoff line is then obtained, this area containing the overhead lights. The regulatory requirements are then satisfied, but the light intensity diffused in the rectangle is such that it is unpleasant—or even a nuisance—for the driver.
A second known solution consists of slightly frosting the entry face of the lens 105. Some of the light signals are thus diverted from their initial path and some are emitted in the direction of the overhead lights. However, such a method has several drawbacks: firstly the frosted surface diffuses light almost isotropically, a large quantity of energy being wasted, including in areas of the beam where the intensity is already relatively low; secondly, the production of molds for obtaining a frosted surface is very tricky, the mold itself being little by little polished by the glass used to manufacture the lens. In practice, it is therefore necessary to carry out a surfacing operation in order to obtain a slightly frosted face, this operation following the molding operation.